1. Field of the Invention
The present invention relates to suspensions for producing filled cast resins, especially those based on (meth)acrylates, that have a low viscosity, a low tendency toward structural viscosity or sedimentation of the filler particles, and provide castings having excellent flame resistance and climate stability.
2. Discussion of the Background
Filled cast resins, especially those from (meth)acrylates, from which castings with high flame resistance and high climate stability can be produced are known.
German Patent 2,449,656 (corresponding to U.S. Pat. Nos. 4,221,697 and 4,251,576), describes stable, flowable, moldable, and hardenable masses consisting of a polymerizable organic fluid and particle-shaped, inorganic fillers obtained by dispersing a filler in the polymerizable fluid that contains a polymer dispersing agent and potentially a low-molecular weight binder, as well as other polymer components. The filler concentration can be 20 to 90% by volume, with silicon dioxide and aluminum oxide preferred as fillers and acrylates or methacrylates preferred as polymerizable fluids.
The mixtures cited in European Patent Application 0,197,682 (corresponding to U.S. Pat. No. 3,847,865) contain unsaturated urethanes, methylmethacrylate, thermoplasts, and potentially, 30 to 70 percent by weight of fillers. The fillers include silicon dioxide, calcium carbonate, talcum, alumina, or aluminum hydrate, with the use of "coupling agents", such as silanes, to bind the filler to the polymer matrix, herein preferred.
European Patent 0,218,866 (corresponding to U.S. Pat. No. 4,786,660) describes a process for producing hardenable cast resins, based on esters of (meth)acrylic acid, containing high portions of finely divided inorganic fillers and which use organosilicon compounds as coupling agents. The resulting thixotropic suspension is transformed by standing or brief heating into a fully deflocculated low-viscosity suspension.
European Patent 0,214,551 (corresponding to U.S. Pat. No. 4,826,901) describes hardenable cast resins based on flowable, hardenable polymer precursors with a content of finely divided inorganic fillers of 20 to 80% by weight and a polymerizable organosilicon compound as coupling agent. The liquid phase formed from the organic components contains an amount of lecithin of from 0.01 to 5% by weight.
German Patent 2,006,197 relates to fire-resistant, impact-resistant castings obtained by polymerization of methylmethacrylate or copolymerization of at least 50% by weight of methylmethacrylate with .alpha., .beta.-ethylene-unsaturated compounds in the presence of a water-soluble catalyst, a filler based on aluminum oxide and a small amount of water. The castings thus prepared contain 20 to 85% by weight aluminum oxide hydrate or aluminum hydroxide.
The aluminum hydroxide-filled cast resins based on methacrylates according to European Patent Application 0,253,211 (corresponding to U.S. Pat. No. 4,771,095) have a high content of aluminum hydroxide or aluminum oxide hydrate as a filler. The disclosed cast resins contain a mixture of at least one organosilicon compound with functional group, a silicon ester, and an organic metallic acid compound each. In the unhardened state, such cast resins have viscosities that are clearly lower than the viscosities of known analogous cast resins which do not contain the disclosed mixture.
A number of Japanese disclosures describe cast resins based on methylmethacrylate with aluminum hydroxide as a filler, and potentially organosilicon compounds as coupling agents (see Japan. Kokai Tokkyo Koho 78/115,768, JP 60/199,616, JP 61/141,653, JP 61/209,202, JP 63/222,057, JP 63/221,151, and Japanese Kokai Tokkyo Koho JP 01/014,188.
These Japanese castings possess a marble-like appearance and good fire-resistance.
European Patent Application 211,657 (corresponding to U.S. Pat. No. 4,734,452) describes hardenable compositions of a monomer mixture consisting of an aliphatic, polyfunctional (meth)acrylate and an aromatic vinyl compound, an inorganic filler with a maximum particle diameter of 5 .mu.m, and a catalytic content of polymerization initiator. Preferred inorganic fillers are hydrated metal oxides, e.g. aluminum hydroxide.
WO 89/05,310 describes castings made by polymerization of a stable, liquid mixture consisting of a methylmethacrylate syrup, aluminum hydroxide filler particles, and a coupling agent. The disclosed castings can be used as kitchen sinks that have a good hot water/cold water alternation stability.
German Offenlegungsschrift 3,826,183 describes flame-resistant to non-flammable, plastic-modified dispersion plasters and synthetic dispersion adhesives that consist essentially of 39 to 57% by weight of plate-like hydrargillite Al(OH), as a mixture of a component with a median particle diameter of 0.5 to 40 .mu.m and a component with a median particle diameter between 40 and 150 .mu.m, as well as plastic dispersion fillers consisting of 63 to 74% by weight of plate-like hydrargillite composed of three components with various median particle diameters.
The large filler particles (particle sizes &gt;30 .mu.m) used in the above-cited references provide suspensions having high filler content with relatively low viscosity in the suspension. However, the resulting suspensions show a strong tendency for sedimentation of the filler. Consequently, the castings formed from these cast resins are inhomogeneous. These inhomogeneities caused by sedimentation cause deformations in the desired shape of the castings, which in the case of the production of cast plates is seen as sagging of the cast plate.
If small filler particles (particle size &lt;5 .mu.m), such as those described in the above references, are used, filler contents of more than 60% by weight in the suspension tend to cause a sharp rise in viscosity that prohibits pourability and exhibits a distinct structurally viscous behavior. As a result of this, inhomogeneities again occur in the cast resin castings, again due to gas inclusion (e.g. air bubbles) in the suspension that are difficult to remove even upon application of a vacuum.